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981.
982.
983.
Cautionary note on the use of [methyl-3H]thymidine to measure rates of chloroplast DNA synthesis in Chlamydomonas reinhardtii 总被引:2,自引:0,他引:2 下载免费PDF全文
Commercial [methyl-3H]thymidine preparations tested here contain about a 0.2% contaminant which is rapidly incorporated into Chlamydomonas DNA. This contaminant obscures the measurement of the rate of chloroplast DNA synthesis when methyl-labeled preparations are used. Such contaminants are not present in ring-labeled (either 3H or 14C) thymidine preparations. In ring-labeled thymidine preparations, a slower incorporation rate commensurate with cell density is observed. These slower, long-term incorporation kinetics would be expected for the utilization of bona fide thymidine into chloroplast DNA. 相似文献
984.
Comparison of the sugar intake of 1,158 men believed to be free of ischaemic heart disease failed to establish any real difference in intake when compared with 170 men with confirmed or possible ischaemic heart disease. In neither group was mere any significant correlation between sugar intake and serum cholesterol, white blood cell count, haemoglobin, E.S.R., β-lipoprotein, or uric add; nor was there any correlation between total sugar intake and weight gain after the age of 25 years.These results suggest that considerably more confirmation is required before acceptance of Yudkm''s hypothesis that high sugar intake is the chief dietary factor causing ischaemic heart disease. 相似文献
985.
986.
The relationship between the F.E.V.1 as an index of airways obstruction and Pco2 as an index of hypoventilation was investigated in 13 patients with chronic obstructive airways disease. Patients who had a normal Pco2 despite severe airways obstruction retained relatively normal sensitivity to CO2 as assessed by their “inspiratory mechanical work rate” response to CO2. Others showed a raised Pco2 in the presence of lesser degrees of airways obstruction and had reduced sensitivity to CO2. 相似文献
987.
Tsai H Howell T Nitcher R Missirian V Watson B Ngo KJ Lieberman M Fass J Uauy C Tran RK Khan AA Filkov V Tai TH Dubcovsky J Comai L 《Plant physiology》2011,156(3):1257-1268
Discovery of rare mutations in populations requires methods, such as TILLING (for Targeting Induced Local Lesions in Genomes), for processing and analyzing many individuals in parallel. Previous TILLING protocols employed enzymatic or physical discrimination of heteroduplexed from homoduplexed target DNA. Using mutant populations of rice (Oryza sativa) and wheat (Triticum durum), we developed a method based on Illumina sequencing of target genes amplified from multidimensionally pooled templates representing 768 individuals per experiment. Parallel processing of sequencing libraries was aided by unique tracer sequences and barcodes allowing flexibility in the number and pooling arrangement of targeted genes, species, and pooling scheme. Sequencing reads were processed and aligned to the reference to identify possible single-nucleotide changes, which were then evaluated for frequency, sequencing quality, intersection pattern in pools, and statistical relevance to produce a Bayesian score with an associated confidence threshold. Discovery was robust both in rice and wheat using either bidimensional or tridimensional pooling schemes. The method compared favorably with other molecular and computational approaches, providing high sensitivity and specificity. 相似文献
988.
Here we describe a protocol for generating 3D human intestinal tissues (called organoids) in vitro from human pluripotent stem cells (hPSCs). To generate intestinal organoids, pluripotent stem cells are first differentiated into FOXA2(+)SOX17(+) endoderm by treating the cells with activin A for 3 d. After endoderm induction, the pluripotent stem cells are patterned into CDX2(+) mid- and hindgut tissue using FGF4 and WNT3a. During this patterning step, 3D mid- or hindgut spheroids bud from the monolayer epithelium attached to the tissue culture dish. The 3D spheroids are further cultured in Matrigel along with prointestinal growth factors, and they proliferate and expand over 1-3 months to give rise to intestinal tissue, complete with intestinal mesenchyme and epithelium comprising all of the major intestinal cell types. To date, this is the only method for efficiently directing the differentiation of hPSCs into 3D human intestinal tissue in vitro. 相似文献
989.
Although the septin ring and collar in budding yeast were described over 20 years ago, there is still controversy regarding the organization of septin filaments within these structures and about the way in which the ring first forms and about how it converts into a collar at the mother-bud neck. Here we present quantitative analyses of the recruitment of fluorescently-tagged septins to the ring and collar through the cell cycle. Septin ring assembly began several minutes after polarity establishment and this interval was longer in daughter than in mother cells, suggesting asymmetric inheritance of septin regulators. Septins formed an initial faint and irregular ring, which became more regular as septins were recruited at a constant rate. This steady rate of septin recruitment continued for several minutes after the ring converted to a collar at bud emergence. We did not detect a stepwise change in septin fluorescence during the ring-to-collar transition. After collar formation, septins continued to accumulate at the bud neck, though at a reduced rate, until the onset of cytokinesis when the amount of neck-localized septins rapidly decreased. Implications for the mechanism of septin ring assembly are discussed. 相似文献
990.
In fibroblasts and keratocytes, motility is actin dependent, while microtubules play a secondary role, providing directional guidance. We demonstrate here that the motility of glioblastoma cells is exceptional, in that it occurs in cells depleted of assembled actin. Cells display persistent motility in the presence of actin inhibitors at concentrations sufficient to fully disassemble actin. Such actin independent motility is characterized by the extension of cell protrusions containing abundant microtubule polymers. Strikingly, glioblastoma cells exhibit no motility in the presence of microtubule inhibitors, at concentrations that disassemble labile microtubule polymers. In accord with an unconventional mode of motility, glioblastoma cells have some unusual requirements for the Rho GTPases. While Rac1 is required for lamellipodial protrusions in fibroblasts, expression of dominant negative Rac1 does not suppress glioblastoma migration. Other GTPase mutants are largely without unique effect, except dominant positive Rac1-Q61L, and rapidly cycling Rac1-F28L, which substantially suppress glioblastoma motility. We conclude that glioblastoma cells display an unprecedented mode of intrinsic motility that can occur in the absence of actin polymer, and that appears to require polymerized microtubules. 相似文献